1. Field of the Invention
This invention relates to coatings, and especially to circuit board coatings and processes. In this invention, a single coating material can serve as a corrosion inhibitor, a no-clean soldering flux, and/or a protective coating in replacement of a conformal coating. In its most preferred form, this invention serves all three functions. The invention also involves compositions, and products other than circuit boards too.
2. Prior Art
As indicated above, this invention is remarkable in that it is useful in any one or all of three separate phases of electronic circuit board manufacturing. The first phase involves manufacture of the circuit board itself, which is referred to herein as circuit board fabrication. This first phase delineates a copper circuit pattern on a non-conductive plastic substrate or support layer. The second phase of electronic circuit board manufacturing involves the soldering of components to the copper circuit pattern that was previously delineated on the circuit board. The third phase of electronic circuit board manufacturing involves treatment of the board after soldering, as for example applying a conformal coating to the assembled board.
The fact that this invention is useful in the second, or soldering, phase of electronic circuit board manufacturing is remarkable, in and of itself. The reason why it is remarkable, is that it provides a special type of soldering flux, as will more fully be hereinafter explained. This special type of flux is referred to herein as a no-clean flux. By no-clean, we mean that at least chlorofluorocarbons (CFCs) and other chlorinated organic solvents are not needed to remove flux residue after soldering. Water rinsing may even be unnecessary. This, alone, is significant. The electronics industry is trying to avoid using fluxes that leave residues that must be cleaned off, especially if they must be cleaned off using CFC and/or chlorinated solvents. Tests indicate that this invention leaves such little ionic residue that no cleaning at all may be needed for most applications.
In the first phase of electronic circuit board manufacturing, i.e., the fabrication phase, this invention involves applying a coating to the copper conductor pattern after the pattern is delineated on its insulating organic-based substrate material, and before components are soldered to it. The purpose of our coating in this phase of manufacturing is for preventing oxidation of the exposed surfaces of the copper pattern. More will be said about this later in this specification. If the board is stored for any length of time in air, the exposed surface of the copper film can oxidize. More will be said about this first aspect of the invention in the following detailed description of the invention.
As indicated above, the second phase of electronic circuit board manufacturing involves the soldering of electrical components to the board. In this second aspect of our invention, our coating can serve as a soldering flux. Even better, it can serve as a no-clean soldering flux. Even if the soldering requirement needs an added flux, our coating is wettable by molten solder. Hence, it need not be removed prior to soldering if it was previously applied as an antioxidant for the copper pattern in the first phase of manufacturing. In addition, organic acid activators can be added to the coating used in the first phase of manufacturing, to enhance fluxing action during the soldering phase. With the proper choice of activators, low ionic residues can still be obtained. More will be said about these features in the detailed description.
In the third phase of electronic circuit board manufacturing, one applies a conformal coating to the substantially completed board. By conformal coating, we mean a thick coating, usually polymeric, that is applied to an otherwise finished circuit board to protect the board from corrosion in humid environments. Our coating is more than just compatible with conformal coatings. In many instances, it passivates the copper surfaces well enough by itself to eliminate the need for a conformal coating.
All will be understood, the elimination of processing steps eliminates the direct costs of performing such steps. However, it also eliminates the indirect costs of apparatus needed for the steps, factory floor space, etc.